Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Generating an audio signal associated with a virtual sound
source
FIELD OF THE INVENTION
This disclosure relates to a method and system for
generating an audio signal associated with a virtual sound
source. In particular to such method and system wherein an
input audio signal x(t) is modified to obtain a modified audio
signal and wherein the modification comprises performing a
signal delay operation. The audio signal y(t) is generated
based on a combination, e.g. a summation, of the input audio
signal x(t) and the modified audio signal.
BACKGROUND
In the playback of sound through audio transmitters, i.e.
loudspeakers, much of the inherent spatial information of the
(recorded) sound is lost. Therefore, the experience of sound
through speakers is often felt to lack depth (it sounds
'flat') and dimensionality (it sounds 'in-the-box'). The
active perception of height is altogether missing from the
sound experience across the speakers. These conditions create
an inherent detachment between the listener and sound in the
environment. This creates an obstacle for the observer to
fully identify physically and emotionally with the sound
environment and in general this makes sound experiences more
passive and less engaging.
A classical demonstration of this problem is described by
Von Bekesy's (Experiments in Hearing, 1960): the 'in-the-box'
sound effect seems to increase with the decrease of the
loudspeaker's dimensions. In an experimental research on the
relation between acoustic power, spectral balance and
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perceived spatial dimensions and loudness, Von Bekesy's test
subjects were unable to correctly indicate the relative
dimensional shape of a reproduced sound source as soon as the
source's dimensions exceeded the actual shape of the
reproducing loudspeaker box. One may conclude that the
loudspeaker's spatio-spectral properties introduce a message-
media conflict when transmitting sound information. We cannot
recognize the spatial dimensions of the sound source in the
reproduced sound. Instead, we listen to the properties of the
loudspeaker.
In the prior art there is no satisfying approach to record
or compute dimensional information of sound sources. The near-
field information of sound producing objects cannot be
accurately captured by microphones, or would theoretically
require an infinite grid of pressure and particle velocity
transducers to capture the dimensional information of the
object.
For a computational simulation of dimensional information,
solutions to the wave equation are only applicable to a
limited amount of basic geometrical shapes and for a limited
frequency range. Given the lack of an analytical solution to
the problem, simulation models have to resort to finite
computation methods to attempt to reproduce the desired data.
The data gathered in this way and reproduced by means of
techniques involving FFT (Fast Fourier Transform), such as
convolution or additive synthesis, require complex
calculations and very large amounts of data processing and are
thus inherently very intensive for computer processing. This
limits the application of such methods and poses a problem for
the audio playback system that can accurately reproduce the
information.
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Hence, there is a need in the art for a method for
generating audio signals associated with a virtual sound
source that are less computationally expensive.
SUMMARY
To that end, a method for generating an audio signal
associated with a virtual sound source is disclosed. The
method comprising either (i) obtaining an input audio signal
x(t), and modifying the input audio signal x(t) to obtain a
modified audio signal using a signal delay operation
introducing a time delay; and generating the audio signal y(t)
based on a combination, e.g. a summation, of the input audio
signal x(t), or of an inverted and/or attenuated or amplified
version of the input audio signal x(t), and the modified audio
signal. Alternatively (ii), the method comprises obtaining an
input audio signal x(t), and generating the audio signal y(t)
based on a signal feedback operation that recursively adds a
modified version of the input audio signal x(t) to itself,
wherein the signal feedback operation comprises a signal delay
operation introducing a time delay and, optionally, a signal
inverting operation.
When a virtual sound source is said to have a particular
size and shape and/or to be positioned at a particular
distance and/or to be positioned at a particular height or
depth it may be understood as that an observer, when hearing
the generated audio signal, perceives the audio signal as
originating from a sound source having that particular size
and shape and/or being positioned at said particular distance
and/or at said particular height or depth. The human hearing
is very sensitive, as also illustrated by the Von Bekesy
experiment described above, to spectral information that
correlates with the dimensions of the object producing the
sound. The human hearing recognizes the features of a sounding
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object primarily by its resonance, i.e. the amplification of
one or several fundamental frequencies and their correlating
higher harmonics, such amplification resulting from standing
waves that occur inside the object or space due to its
particular size and shape. By adding and subtracting spectral
information from the audio signal in such a way that its
resulting spectrum will closely resemble the resonance of the
intended object or space, one can at least partially overrule
the spatio-spectral properties of the loudspeaker(s) and
create a coherent spatial projection of the sound signal by
means of its size and shape. The applicant has realized that
such spatial information, related to the dimensions of a sound
source and its virtual distance, height and depth in relation
to an observer, can be added to an audio signal by performing
relatively simple operations onto an input audio signal. In
particular, the applicant has found that these simple
operations are sufficient for generating an audio signal
having properties such that the physiology of the human
hearing apparatus causes an observer to perceive the audio
signal as coming from a sound source having a certain position
and dimensions, other than the position and dimensions of the
loudspeakers that produce the sound. The above-described
method does not require filtering or synthesizing individual
(bands of) frequencies and amplitudes to add this spatial
information to the input audio signal. The method thus
bypasses the need for FFT synthesis techniques for such
purpose, in this way simplifying the process and considerably
reducing the processing power required.
Optionally, the method comprises playing back the generated
audio signal, e.g. by providing the generated audio signal to
one or more loudspeakers in order to have the generated audio
signal played back by the one or more loudspeakers.
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The generated audio signal, once played out by a
loudspeaker system, causes the desired perception by an
observer irrespective of how many loudspeakers are used and
irrespective of the position of the observer relative to the
5 loudspeakers.
A signal that is said to have been generated based on a
combination of two or more signals may be the combination,
e.g. the summation, of these two or more signals.
In an example, the generated audio signal is stored onto a
computer readable medium so that it can be played out at a
later time by a loudspeaker system.
The audio signal can be generated in real-time, which may
be understood as that the audio signal is generated
immediately as the input audio signal comes in and/or may be
understood as that any variation in the input audio signal at
a particular time is reflected in the generated audio signal
within three seconds, preferably within 0.5 seconds, more
preferably within 50 ms, most preferably within 10 ms. The
relatively simple operations for generating the audio signal
allows for such real-time processing. Optionally, the
generated audio signal is played back in real-time, which may
be understood as that the audio signal, once generated, is
played back without substantial delay.
In an embodiment, the virtual sound source has a shape.
Such embodiment comprises generating audio signal components
associated with respective virtual points on the virtual sound
source's shape. This step comprises generating a first audio
signal component associated with a first virtual point on the
virtual sound source's shape and a second audio signal
component associated with a second virtual point on the
virtual sound source's shape, wherein either (i)
generating the first audio signal component comprises
modifying the input audio signal to obtain a modified first
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audio signal component using a first signal delay operation
introducing a first time delay and comprises generating the
first audio signal component based on a combination, e.g. a
summation, of the input audio signal or of an inverted and/or
attenuated or amplified version of the input audio signal
x(t), and the modified first audio signal component, or
wherein (ii)
generating the first audio signal component comprises using
a feedback loop that recursively adds a modified version of
the input audio signal x(t) to itself, wherein the feedback
loop comprises a signal delay operation introducing a first
time delay and a signal inverting operation. Further, in this
embodiment, either (i)
generating the second audio signal component comprises
modifying the input audio signal to obtain a modified second
audio signal component using a second signal delay operation
introducing a second time delay different from the first time
delay and comprises generating the second audio signal
component based on a combination, e.g. a summation, of the
input audio signal or of an inverted and/or attenuated or
amplified version of the input audio signal x(t), and the
modified second audio signal component, or wherein (ii)
generating the second audio signal component comprises
using a feedback loop that recursively adds a modified version
of the input audio signal x(t) to itself, wherein the feedback
loop comprises a signal delay operation introducing a second
time delay and a signal inverting operation.
The applicant has found out that this embodiment allows to
add the dimensional information of the virtual sound source to
the input audio signal x(t) in a simple manner, without
requiring complex algorithms, such as FFT algorithms, additive
synthesis of individual frequency bands or multitudes of
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bandpass filters to obtain the desired result, as has been the
case in the prior art.
Preferably, many more than two virtual points may be
defined on the virtual sound source's shape. An arbitrary
number of virtual points may be defined on the shape of the
virtual sound source. For each of these virtual points, an
audio signal component may be determined. Each determination
of audio signal component may then comprise determining a
modified audio signal component using a signal delay operation
introducing a respective time delay. Each audio signal
component may then be determined based on a combination, e.g.
a summation, of its modified audio signal component and the
input audio signal.
Each determination of a modified audio signal component may
further comprise performing a signal inverting operation
and/or a signal amplification or attenuation and/or a signal
feedback operation. Herein, preferably, the signal feedback
operation is performed last. In principle, the signal
inverting operation, amplification/attenuation and signal
delay operation may be performed in any order.
The virtual points may be positioned equidistant from each
other on the shape of the virtual sound source. Further, the
virtual sound source may have any shape, such as a one-
dimensional shape, e.g. a 1D string, a two-dimensional shape,
e.g. a 2D plate shape, or a three-dimensional shape, e.g. a 3D
cube.
The time period with which an audio signal is delayed may
be zero for some audio signal components. To illustrate, if
the virtual sound source is a string, the time delay for the
two virtual points at the respective ends of the string where
its vibration is restricted, may be zero. This will be
illustrated below with reference to the figures.
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In an embodiment, the method comprises obtaining shape data
representing the virtual positions of the respective virtual
points on the virtual sound source's shape and determining the
first resp. second time delay based on the virtual position of
the first resp. second virtual point. Thus, the respective
time delays for determining the respective audio signal
components for the different virtual points may be determined
based on the respective virtual positions of these virtual
points.
The applicant has found out that this embodiment enables to
take into account how sound waves propagate through a
dimensional shape, which enables to accurately generate audio
signals that are perceived by an observer to originate from a
sound source having that particular shape. When generated
audio signal components associated with the virtual points are
played back through a loudspeaker, or distributed across
multiple loudspeakers, the result is perceived as one coherent
sound source in space because the signal components strengthen
their coherence at corresponding wavelengths in harmonic
ratios according to the fundamental resonance frequencies of
the virtual shape. This at least partially overrules the
mechanism of the ear to detect its actual output components,
i.e. the loudspeaker(s).
Preferably, the time period for each time delayed version
of the audio input signal is determined following a
relationship between spatial dimensions and time, examples of
which are given below in the figure descriptions.
In an embodiment, the to be generated audio signal y(t) is
associated with a virtual sound source having a distance from
an observer. This embodiment comprises (i) modifying the input
audio signal using a time delay operation introducing a time
delay and a signal feedback operation to obtain a first
modified audio signal, and (ii) generating a second modified
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audio signal based on a combination of the input audio signal
x(t) and the first modified audio signal; and (iii) generating
the audio signal y(t) based on the second modified audio
signal, this step comprising attenuating the second modified
audio signal and optionally comprising performing a time delay
operation introducing a second time delay.
The human hearing recognizes a sound source distance
detecting primarily the changes in the overall intensity of
the auditory stimulus and the proportionally faster
dissipation of energy from the high to the lower frequencies.
The applicant has found out that this embodiment allows to add
such distance information to the input audio signal in a very
simple and computationally inexpensive manner.
The second introduced time delay may be used to cause a
Doppler effect for the observer. This embodiment further
allows controlling a Q-factor, which narrows or widens the
bandwidth of the resonant frequencies in the signal. In this
case, since the perceived resonant frequency is infinitely low
at the furthest possible virtual distance, the Q-factor
influences the steepness of a curve covering the entire
audible frequency range from high to the low frequencies,
resulting in the intended gradual increase of high-frequency
dissipation in the signal.
Preferably, the time delay introduced by the time delay
operation that is performed to obtain the first modified audio
signal is shorter than 0.00007 seconds, preferably shorter
than 0.00005 seconds, more preferably shorter than 0.00002
seconds, most preferably approximately 0.00001 seconds.
The second modified audio signal may be attenuated in
dependence of the distance of the virtual sound source. For
the signal feedback operation that is performed in order to
determine the first modified audio signal, in which an
attenuated version of a signal is recursively added to itself,
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the signal attenuation is preferably also performed in
dependence of said distance. Optionally, such embodiment
comprises obtaining distance data representing the distance of
the virtual sound source so that the attenuation can be
5 automatically appropriately controlled. This embodiment allows
to "move" the virtual sound source towards and away from an
observer by simply adjusting a few values.
In the above embodiment, the signal feedback operation
comprises attenuating a signal, e.g. the signal as obtained
10 after performing the time delay operation introducing said
time delay, and recursively adding the attenuated signal to
the signal itself. Such embodiment may further comprise
controlling the degree of attenuation in the signal feedback
operation and the degree of attenuation of the second modified
audio signal in dependence of said distance, such that the
larger the distance is, the lower the degree of attenuation in
the signal feedback operation and the higher the degree of
attenuation of the second modified audio signal.
In an embodiment, the virtual sound source has a distance
from an observer. This embodiment comprises modifying the
input audio signal to obtain a first modified audio signal
using a signal feedback operation that recursively adds a
modified version of the input audio signal to itself, wherein
the feedback operation comprises a signal delay operation
introducing a time delay, and generating the audio signal y(t)
based on the first modified audio signal, this step comprising
a signal attenuation and optionally a time delay operation
introducing a second time delay, wherein, optionally, the
embodiment further comprises generating a second modified
audio signal based on a combination of the first modified
audio signal and a time-delayed version of the first modified
audio signal and generating the audio signal (y(t) based on
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the second modified audio signal thus based on the first
modified audio signal.
The above considerations about the introduced time delays,
also apply to the attenuation in this embodiment.
In an embodiment, in which the virtual sound source is
positioned at a distance from an observer, and in which the
second modified audio signal is attenuated in dependence of
the distance, modifying the input audio signal to obtain the
first modified audio signal comprises a particular signal
attenuation. This embodiment comprises controlling the degree
of attenuation of the particular signal attenuation and the
degree of attenuation of the second modified audio signal in
dependence of said distance, such that the larger the distance
is, the lower the degree of attenuation of the particular
signal attenuation and the higher the degree of attenuation of
the second modified audio signal.
In an embodiment, the to be generated audio signal y(t)
associated with a virtual sound source is positioned at a
virtual height above an observer. In such embodiment, the
method comprises (i) modifying the input audio signal x(t)
using a signal inverting operation, a signal attenuation
operation and a time delay operation introducing a time delay
in order to obtain a third modified audio signal, and (ii)
generating the audio signal based on a combination, e.g. a
summation, of the input audio signal and the third modified
audio signal.
The applicant has found out that this embodiment allows to,
in a simple manner, generate audio signals that come from a
virtual sound source positioned at a certain height.
In this embodiment, the introduced time delay is preferably
shorter than 0.00007 seconds, preferably shorter than 0.00005
seconds, more preferably shorter than 0.00002 seconds, most
preferably approximately 0.00001 seconds.
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In the above embodiment, modifying the input audio signal
to obtain the third modified audio signal optionally comprises
performing a signal feedback operation. In a particular
example, this step comprises recursively adding an attenuated
version of a signal, e.g. the signal resulting from the time
delay operation, signal attenuation operation and signal
inverting operation that are performed to eventually obtain
the third modified audio signal, to itself.
In an embodiment, the to be generated audio signal is
associated with a virtual sound source that is positioned at a
virtual depth below an observer. Such embodiment comprises
modifying the input audio signal x(t) using a time delay
operation introducing a time delay, a signal attenuation
operation and a signal feedback operation in order to obtain a
sixth modified audio signal. Performing the signal feedback
operation e.g. comprises recursively adding an attenuated
version of a signal, e.g. the signal resulting from the time
delay operation and signal attenuation operation that are
performed to eventually obtain the sixth modified audio
signal, to itself. This embodiment further comprises
generating the audio signal based on a combination of the
input audio signal and the sixth modified audio signal.
In an embodiment, the virtual sound source is positioned at
a virtual depth below an observer. This embodiment comprises
generating the audio signal y(t) using a signal feedback
operation that recursively adds a modified version of the
input audio signal to itself, wherein the feedback operation
comprises a signal delay operation introducing a time delay
and a first signal attenuation operation.
In an embodiment, the virtual sound source is positioned at
a virtual depth below an observer. This embodiment comprises
modifying the input audio signal to obtain a sixth modified
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audio signal using a signal feedback operation that
recursively adds a modified version of the input audio signal
to itself, wherein the feedback operation comprises a signal
delay operation introducing a time delay and a first signal
attenuation, and generating the audio signal based on a
combination of the sixth modified audio signal and time-
delayed and attenuated version of the sixth modified audio
signal.
In the above embodiments in which the virtual sound source
is positioned at a virtual depth, the introduced time delay is
preferably shorter than 0.00007 seconds, preferably shorter
than 0.00005 seconds, more preferably shorter than 0.00002
seconds, most preferably approximately 0.00001 seconds.
In an embodiment, the method comprises receiving a user
input indicative of the virtual sound source's shape and/or
indicative of respective virtual positions of virtual points
on the virtual sound source's shape and/or indicative of the
distance between the virtual sound source and the observer
and/or indicative of the height at which the virtual sound
source is positioned above the observer and/or indicative of
the depth at which the virtual sound source is positioned
below the observer. This embodiment allows a user to input
parameters relating to the virtual sound source, which allows
to generate the audio signal in accordance with these
parameters. This embodiment may comprise determining values of
parameters as described herein and using these determined
parameters to generate the audio signal.
In an embodiment, the method comprises generating a user
interface enabling a user to input at least one of:
-the virtual sound source's shape,
-respective virtual positions of virtual points on the
virtual sound source's shape,
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-the distance between the virtual sound source and the
observer,
-the height at which the virtual sound source is positioned
above the observer,
-the depth at which the virtual sound source is positioned
below the observer. This allows a user to easily input
parameters relating to the virtual sound source and as such
allows a user to easily control the virtual sound source.
The methods as described herein may be computer-implemented
methods.
One aspect of this disclosure relates to a computer
comprising a computer readable storage medium having computer
readable program code embodied therewith, and a processor,
preferably a microprocessor, coupled to the computer readable
storage medium, wherein responsive to executing the computer
readable program code, the processor is configured to perform
one or more of the method steps as described herein for
generating an audio signal associated with a virtual sound
source.
One aspect of this disclosure relates to a computer program
or suite of computer programs comprising at least one software
code portion or a computer program product storing at least
one software code portion, the software code portion, when run
on a computer system, being configured for executing one or
more of the method steps as described herein for generating an
audio signal associated with a virtual sound source.
One aspect of this disclosure relates to a computer non-
transitory computer-readable storage medium storing at least
one software code portion, the software code portion, when
executed or processed by a computer, is configured to perform
one or more of the method steps as described herein for
generating an audio signal associated with a virtual sound
source.
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One aspect of this disclosure relates to a user interface
as described herein.
As will be appreciated by one skilled in the art, aspects
of the present invention may be embodied as a system, method
5 or computer program product. Accordingly, aspects of the
present invention may take the form of an entirely hardware
embodiment, an entirely software embodiment (including
firmware, resident software, micro-code, etc.) or an
embodiment combining software and hardware aspects that may
10 all generally be referred to herein as a "circuit," "module"
or "system". Functions described in this disclosure may be
implemented as an algorithm executed by a microprocessor of a
computer. Furthermore, aspects of the present invention may
take the form of a computer program product embodied in one or
15 more computer readable medium(s) having computer readable
program code embodied, e.g., stored, thereon.
Any combination of one or more computer readable medium(s)
may be utilized. The computer readable medium may be a
computer readable signal medium or a computer readable storage
medium. A computer readable storage medium may be, for
example, but not limited to, an electronic, magnetic, optical,
electromagnetic, infrared, or semiconductor system, apparatus,
or device, or any suitable combination of the foregoing. More
specific examples (a non- exhaustive list) of the computer
readable storage medium would include the following: an
electrical connection having one or more wires, a portable
computer diskette, a hard disk, a random access memory (RAM),
a read-only memory (ROM), an erasable programmable read-only
memory (EPROM or Flash memory), an optical fiber, a portable
compact disc read-only memory (CD-ROM), an optical storage
device, a magnetic storage device, or any suitable combination
of the foregoing. In the context of this document, a computer
readable storage medium may be any tangible medium that can
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contain, or store a program for use by or in connection with
an instruction execution system, apparatus, or device.
A computer readable signal medium may include a propagated
data signal with computer readable program code embodied
therein, for example, in baseband or as part of a carrier
wave. Such a propagated signal may take any of a variety of
forms, including, but not limited to, electro-magnetic,
optical, or any suitable combination thereof. A computer
readable signal medium may be any computer readable medium
that is not a computer readable storage medium and that can
communicate, propagate, or transport a program for use by or
in connection with an instruction execution system, apparatus,
or device.
Program code embodied on a computer readable medium may be
transmitted using any appropriate medium, including but not
limited to wireless, wireline, optical fiber, cable, RF, etc.,
or any suitable combination of the foregoing. Computer program
code for carrying out operations for aspects of the present
invention may be written in any combination of one or more
programming languages, including a functional or an object
oriented programming language such as Java(TM), Scala, C++,
Python or the like and conventional procedural programming
languages, such as the "C" programming language or similar
programming languages. The program code may execute entirely
on the user's computer, partly on the user's computer, as a
stand-alone software package, partly on the user's computer
and partly on a remote computer, or entirely on the remote
computer, server or virtualized server. In the latter
scenario, the remote computer may be connected to the user's
computer through any type of network, including a local area
network (LAN) or a wide area network (WAN), or the connection
may be made to an external computer (for example, through the
Internet using an Internet Service Provider).
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Aspects of the present invention are described below with
reference to flowchart illustrations and/or block diagrams of
methods, apparatus (systems), and computer program products
according to embodiments of the invention. It will be
understood that each block of the flowchart illustrations
and/or block diagrams, and combinations of blocks in the
flowchart illustrations and/or block diagrams, can be
implemented by computer program instructions. These computer
program instructions may be provided to a processor, in
particular a microprocessor or central processing unit (CPU),
or graphics processing unit (GPU), of a general purpose
computer, special purpose computer, or other programmable data
processing apparatus to produce a machine, such that the
instructions, which execute via the processor of the computer,
other programmable data processing apparatus, or other devices
create means for implementing the functions/acts specified in
the flowchart and/or block diagram block or blocks.
These computer program instructions may also be stored in a
computer readable medium that can direct a computer, other
programmable data processing apparatus, or other devices to
function in a particular manner, such that the instructions
stored in the computer readable medium produce an article of
manufacture including instructions which implement the
function/act specified in the flowchart and/or block diagram
block or blocks.
The computer program instructions may also be loaded onto a
computer, other programmable data processing apparatus, or
other devices to cause a series of operational steps to be
performed on the computer, other programmable apparatus or
other devices to produce a computer implemented process such
that the instructions which execute on the computer or other
programmable apparatus provide processes for implementing the
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functions/acts specified in the flowchart and/or block diagram
block or blocks.
The flowchart and block diagrams in the figures illustrate
the architecture, functionality, and operation of possible
implementations of systems, methods and computer program
products according to various embodiments of the present
invention. In this regard, each block in the flowchart or
block diagrams may represent a module, segment, or portion of
code, which comprises one or more executable instructions for
implementing the specified logical function(s). It should also
be noted that, in some alternative implementations, the
functions noted in the blocks may occur out of the order noted
in the figures. For example, two blocks shown in succession
may, in fact, be executed substantially concurrently, or the
blocks may sometimes be executed in the reverse order,
depending upon the functionality involved. It will also be
noted that each block of the block diagrams and/or flowchart
illustrations, and combinations of blocks in the block
diagrams and/or flowchart illustrations, can be implemented by
special purpose hardware-based systems that perform the
specified functions or acts, or combinations of special
purpose hardware and computer instructions.
The invention will be further illustrated with reference to
the attached drawings, which schematically will show
embodiments according to the invention. It will be understood
that the invention is not in any way restricted to these
specific embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the invention will be explained in greater
detail by reference to exemplary embodiments shown in the
drawings, in which:
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FIG. 1A-1I illustrate methods and systems according to
respective embodiments;
FIG. 2 shows spectrograms of audio signals generated using
a method and/or system according to an embodiment;
FIG. 3A shows an virtual sound source according to an
embodiment, in particular a virtual sound source shape as a
string;
FIG. 3B schematically shows the input audio signal and
signal inverted, time-delayed versions of the input audio
signal that may be involved in embodiments;
FIG. 4 illustrates a method for adding dimensional
information to the audio signal, the dimensional information
relating to a shape of the virtual sound source;
FIG. 5 illustrates a panning system that may be used in an
embodiment;
FIG. 6A illustrates two-dimensional and three-dimensional
virtual sound sources;
FIG. 6B shows an input signal and time-delayed version of
this signal which may be involved in embodiments;
FIG. 7A illustrates a method for generating an audio signal
associated with a two-dimensional virtual sound source, such
as a plate;
FIG. 7B schematically shows how several parameters may be
determined that are used in an embodiment;
FIGs. 7C and 7D illustrate embodiments that are alternative
to the embodiment of FIG. 7A;
FIG. 8A and 8B show spectrograms of respective audio signal
components associated with respective virtual points on a
virtual sound source;
FIG. 9A and 9B illustrate the generation of a virtual sound
source that is positioned at a distance from an observer
according to an embodiment;
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FIGs 9C-9D show alternative embodiments to the embodiment
of FIG. 9A;
FIG. 10 shows spectrograms associated with a virtual sound
source that is positioned at respective distances;
5 FIG. 11A and 11B illustrate the generation of a virtual
sound source that is positioned at a height above the observer
according to an embodiment;
FIG. 12 shows spectrograms associated with a virtual sound
source that is positioned at respective heights;
10 FIG. 13A and 13B illustrate the generation of a virtual
sound source that is positioned at a depth below the observer
according to an embodiment;
FIGs 13C-13F show alternative embodiments to the embodiment
of FIG. 13A;
15 FIG. 14 illustrates the generation of an audio signal
associated with a virtual sound source having a certain shape,
positioned at a certain position.
FIG. 15 illustrates a user interface according to an
embodiment;
20 FIG. 16 illustrates a data processing system according to
an embodiment.
DETAILED DESCRIPTION OF THE DRAWINGS
Sound waves inherently carry detailed information about the
environment, and about the observer of sound within the
environment. This disclosure describes a soundwave
transformation (spatial wave transform, or SWT), a method for
generating an audio signal, that is perceived to have
spatially coherent properties with regards to the dimensional
size and shape of the reproduced sound source, its relative
distance towards the observer, its height or depth above or
below the observer and its directionality if the source is
moving towards or away from the observer.
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Typically, the spatial wave transform is an algorithm
executed by a computer with as input a digital audio signal
(e.g. a digital recording) and as output one or multiple
modified audio signal(s) which can be played back on
conventional audio playback systems. Alternatively, the
transform could also apply to analogue (non-digital) means of
generating and/or processing audio signal(s). Playing back the
modified sound signal(s) will give the observer an improved
perception of dimensional size and shape of the reproduced
sound source (f.i. a recorded signal of a violin will sound as
if the violin is physically present) and the sound source's
spatial distance, height and depth in relation to the observer
(f.i. the violin sounds at distinctive distance from the
listener, and height above or depth below), while masking the
physical properties of the sound output medium, i.e. the
loudspeaker(s) (that is, the violin does not sound as if it is
coming from a speaker).
Fig. 1A is a flow chart depicting a method and/or system
according to an embodiment. An input audio signal x(t) is
obtained. The input audio signal x(t) may be analog or
digital. Thus, the operations that are shown in figure 1, i.e.
each of the operations 4, 6, 8, 10, 12, 14, may be performed
by an analog circuit component or a digital circuit component.
The flow chart of figure 1 may also be understood to depict
method steps that can be performed by a computer executing
appropriate software code.
The input audio signal x(t) may have been output by a
recording process in which sounds have been recorded and
optionally converted into a digital signal. In an example, a
musical instrument, such as a violin, has been recorded in a
studio to obtain the audio signal that is input for the method
for generating the audio signal as described herein.
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The input audio signal x(t) is subsequently modified to
obtain a modified audio signal. The signal modification
comprises a signal delay operation 4 and/or a signal inverting
operation 6 and/or a signal amplification or attenuation 8
and/or a signal feedback operation 10,12.
The signal delay operation 4 may be performed using well-
known components, such as a delay line. The signal inverting
operation 6 may be understood as inverting a signal such that
an input signal x(t) is converted into -x(t). The
amplification or attenuation 8 may be a linear amplification
or attenuation, which may be understood as amplifying or
attenuating a signal by a constant factor a, such that a
signal x(t) is converted into a * x(t).
The signal feedback operation may be understood to comprise
recursively combining a signal with an attenuated version of
itself. This is schematically depicted by the attenuation
operation 12 that sits in the feedback loop and the combining
operation 10. Decreasing the attenuation, i.e. enlarging
constant b in figure 1A, may increase the peak intensity and
narrow the bandwidth of resonance frequencies in the spectrum
of the sound, the so-called Q-factor. Herewith, the response
of different materials to vibrations can be simulated based on
their density and stiffness. For instance, the response of a
metal object will generate a higher Q-factor than an object of
the same size and shape made out of wood.
The combining operations 10 and 14 may be understood to
combine two or more signals {x1 (t), ..., xn(t)}. The input
signals may be converted into a signal y(t) as follows.
In figure 1A, the audio signal y(t) is generated based on a
combination, e.g. a summation, of the input audio signal x(t)
and the modified audio signal. In an example, the audio signal
y(t) is the result of combining, e.g. summing, the input audio
signal x(t) and the modified audio signal.
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The transformation of the input audio signal x(t) to the
audio signal y(t) may be referred to hereinafter as the
Spatial Wave Transform (SWT).
The method for generating the audio signal y(t) does not
require finite computational methods, such as methods
involving Fast Fourier Transforms, which may limit the
achievable resolution of the generated audio signal. Thus, the
method disclosed herein enables to form high-resolution audio
signals. Herein, high-resolution may be understood as a signal
with spectral modifications for an infinite amount of
frequency components. The virtually infinite resolution is
achieved because the desired spectral information does not
need to be computed and modified for each individual frequency
component, as would be the case in convolution or simulation
models, but the desired spectral modification of frequency
components results from the simple summation, i.e. wave
interference of two identical audio signals with a specific
time delay, amplitude and/or phase difference. This operation
results in phase and amplitude differences for each frequency
component in harmonic ratios, i.e. corresponding to the
spectral patterns caused by resonance. The time delays
relevant to the method are typically between 0.00001 - 0.02
seconds, but not excluding longer times.
The generated audio signal y(t) may be presented to an
observer through a conventional audio output medium, e.g. one
or more loudspeakers. The generated audio signal may be
delayed in time and/or attenuated before being output to the
audio output medium.
Figures 1B - 1G show flow charts depicting the method
and/or system according to other embodiments. Herein, figure
1B differs from figure 1A in that the signal inverting
operation and the signal attenuation operation are performed
after the feedback combination 10.
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Further, figures 1C and 1D illustrate respective
embodiments wherein the audio signal y(t) is generated based
on a signal feedback operation that recursively adds a
modified version of the input audio signal x(t) to itself. The
signal feedback operation comprises a signal delay operation
introducing a time delay and a signal inverting operation.
Herein, figure 1C illustrates an embodiment, wherein the
input audio signal is modified using a signal feedback
operation to obtain a modified audio signal, indicated by 11.
In this embodiment, the audio signal y(t) is generated based
on a combination of this modified audio signal and a time-
delayed, inverted version of this modified audio signal,
indicated by 13. As shown in figure 1C, this may be achieved
by feeding the signal that is fed back to combiner 9, also to
combiner 10.
In Figures 1C and 1D, the damping function resulting from
the signal feedback operation is independent of frequency and
therefore, these embodiments may be understood to constitute
all-pass filters.
The embodiment of figure 1E differs from the one shown in
figure 1A in that the signal delay operation, the signal
inverting operation and the attenuation is performed as part
of the signal feedback operation. The embodiment of figure 1E
is especially advantageous in that it yields a harmonic
pattern which comprises a damping function depending on
frequency. Due to this damping function, the higher
frequencies in the signal dampen faster than lower
frequencies.
The embodiment of figure 1F resp. 1G illustrates respective
embodiments wherein the signal attenuation is performed after
respectively before the signal feedback operation. It should
be appreciated that the signal attenuation may be arranged at
any position in the flow diagram and also several signal
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attenuations may be present at respective positions in the
flow diagram.
Figure 1H-1J illustrate respective embodiments wherein the
audio signal y(t) is generated based on a combination 10 of an
5 inverted and/or attenuated or amplified version of the input
audio signal x(t) and a modified audio signal, wherein the
modified audio signal is obtained using a signal delay
operation and a signal feedback operation.
Figure 1H illustrates an embodiment wherein the modified
10 audio signal is combined with an attenuated version of the
input audio signal, figure 11 illustrates an embodiment
wherein the modified audio signal is combined with an inverted
version of the input audio signal and figure 1J illustrates an
embodiment wherein the modified audio signal is combined with
15 an inverted, attenuated version of the input audio signal.
It should be appreciated that the embodiments of figure 1
can be used as building blocks to build more complex
embodiments, as for example shown in figure 4, 7 and 14. Thus,
although these more complex embodiments use as a building
20 block the embodiment of figure 1A, any of the respective
embodiments of figure 1B - 1J may be used as building blocks.
In these complex embodiments, these building blocks, which may
be any of the embodiments of figures 1B - 1J, are indicated by
21.
25 Figure 2 (top) shows the spectrogram of the generated audio
signal when the input audio signal x(t) is white noise, the
introduced time delay by the time delay operation 4 is
-0.00001 sec, the signal inverting operation 6 is performed
and the signal feedback operation 10,12 is not performed.
Figure 2 (middle) shows the spectrogram of the generated
audio signal when the input audio signal x(t) is white noise,
the introduced time delay by the time delay operation 4 is
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-0.00036 sec, the signal inverting operation 6 is performed
and the signal feedback operation 10,12 is not performed.
Figure 2 (bottom) shows the spectrogram of the generated
audio signal when the input audio signal x(t) is white noise,
the introduced time delay by the time delay operation 4 is
-0.00073 sec, the signal inverting operation 6 is performed
and the signal feedback operation 10,12 is not performed.
These figures show that the spectrum of an audio signal can
be modified precisely according to harmonic ratios, using a
very simple operation.
Figure 3A illustrates a virtual sound source in the form of
a string. A number of virtual points n have been defined on
the string's shape, in this example 17 virtual points. The
points may be equidistant from each other as shown. The
regular distance chosen between each two particles determines
the resolution with which the virtual sound source is defined.
Figures 4 and 7 illustrate embodiments of the method and/or
system that may be used to generate an audio signal that is
perceived to originate from a sound source having a particular
shape, e.g. the string shape as shown in figure 3A, the plate-
shaped source or cubic source illustrated in figure 6. In
these embodiments, the method comprises generating audio
signal components y(t) associated with respective virtual
points on the virtual sound source's shape. Generating each
audio signal component y(t) comprises modifying the input
audio signal to obtain a modified audio signal component using
a signal delay operation introducing a time delay Ate. Then,
each audio signal component y(t) is generated based on a
combination, e.g. a summation, of the input audio signal and
its modified audio signal component. Preferably, the amplitude
of each signal component resulting from said combination is
attenuated, e.g. with -6 dB, by signal attenuating elements 191
- 19n. At least two of the time delays that are introduced
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differ from each other. The audio signal components y(t)
together may be understood to constitute the generated audio
signal y(t). In an example, the audio signal components are
combined to generate the audio signal. However, in another
example, these audio signal components are individually fed to
a panning system that distributes each component individually
to a plurality of loudspeakers. When the audio signal
components are played back simultaneously through an audio
output medium, e.g. through one or more loudspeakers, the
resulting audio signal will be perceived by an observer as
originating from a sound source having the particular shape.
Figure 4 in particular illustrates an embodiment for
generating an audio signal that is perceived to originate from
a sound source that is shaped as a string, e.g. the string
shown in figure 3A. Thus, referring to figure 3A, generated
audio signal component yi(t) is associated with point n=1,
audio signal component y2(t) with point n=2, et cetera. In this
embodiment, each modification to the input audio signal not
only comprises the introduction of a time delay Ate, but also
inverting the audio input signal as indicated by signal
inverting operations 161- 16, in order to obtain a modified
audio signal component. The modified audio signal components
are inverted with respect to the input audio signal, in the
case of a sounding object that cannot freely vibrate on its
edges, such as is the case with a string under tension, or the
skin of a drum. In case of a sounding object that freely
vibrates on all its edges, none of the modified audio signal
components are inverted, and preferably a high-pass filter is
added to the resulting signal component y(t) to attenuate the
low frequencies of the audio signal as will be explained with
reference to figure 7.
Optionally, the modification also comprises a signal
feedback operation 181- 18, but this is not required for
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adding the dimensional information of the virtual sound source
to the audio signal. The depicted embodiment shows that each
audio signal component y(t) may be the result of a summation
of the input audio signal x(t) and the inverted, time-delayed
input audio signal. While figure 4 shows that the time delay
operation is performed prior to the signal inverting operation
16, this may be the other way around.
For a string shaped virtual sound source of 1 meter long,
the time differences for 17 equidistant positioned virtual
points on the string may be as follows:
n At (s)
1 0.00000
2 0.00036
3 0.00073
4 0.00109
5 0.00146
6 0.00182
7 0.00219
8 0.00255
9 0.00292
10 0.00255
11 0.00219
12 0.00182
13 0.00146
14 0.00109
0.00073
16 0.00036
17 0.00000
These values for the introduced time delays are in
accordance with Atn=Lxn/v, wherein L indicates the length of
15 the string, wherein xn denotes for virtual point n a
multiplication factor and v relates to the speed of sound
through a medium. For the values in the table, a value of 343
m/s was used, which is the velocity of sound waves moving
through air at 20 degrees Celsius. A virtual point may be
understood to be positioned on a line segment that runs from
the center of the virtual sound source, e.g. the center of a
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string, plate or cube to an edge of the virtual sound source.
As such, the virtual point may be understood to divide the
line segment in two parts, namely a first part of the line
segment that runs between an end of the virtual sound source
and the virtual point and a second part of the line segment
that runs between the virtual point and the center of the
virtual sound source. The multiplication factor may be equal
to the ratio between the length of the line segment's first
part and the length of the line segment's second part.
Accordingly, if the virtual point is positioned at an end of
the sound source, the multiplication factor is zero and if the
virtual point is positioned at the center of the virtual sound
source, the multiplication factor is one. Thus, with these
values, a user will perceive the generated audio signal as
originating from a string-shaped sound source that is one
meter in length, whereas the loudspeakers need not be
spatially arranged in a particular manner.
In an embodiment, the method comprises obtaining shape data
representing the virtual positions of the respective virtual
points on the virtual sound source's shape and determining the
time delays that are to be introduced by the respective time
delay operations based on the virtual positions of the
respective virtual points, preferably in accordance with the
above described formula.
Figure 3B schematically shows modified audio signal
components 222, 223 and 224 for points n=1, 2, 3 respectively.
These audio signal components have been inverted with respect
to the audio input signal 20 and time delayed by At2, At2, At4
respectively.
Although figure 4 shows that the embodiment of figure 1A is
used as building block 21, any of the embodiments shown in
respective figures 1A - 1J may be used.
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Figure 5 shows that the generated audio signal, or the
generated audio signal components together forming the
generated audio signal can be panned to one or more
loudspeakers. This panning step may be performed using methods
5 known in the art. In principle, with the method disclosed
herein, the spatial information regarding dimensions,
distance, height and depth of the virtual sound source can be
added to an audio signal irrespective of the panning method
and irrespective of how many loudspeakers are used to playback
10 the audio signal.
In an embodiment, each of the generated audio signal
components may in principle be fed to all loudspeakers that
are present. However, depending on the panning method that is
used, some of the audio signal components may be fed to a
15 loudspeaker with zero amplification. Herewith, effectively,
such loudspeaker does not receive such audio signal component.
This is depicted in figure 5 for yl in relation to loudspeaker
C and D, for y2 in relation to loudspeakers A and D, and for
y3 in relation to loudspeaker A. Typically, a panning system
20 will provide the audio signal components to the loudspeakers
with a discrete amplification of each audio signal component
to each loudspeaker between zero and one.
Fig. 6A depicts further examples of virtual sound sources
in order to illustrate that the method may be used for virtual
25 sound sources having a more complex shape. The generated audio
signal y(t) may for example be perceived as originating from a
plate-shaped sound source 24 or a cubic-shaped sound source
26. Virtual points are defined onto the shape of the virtual
sound source. A total of twenty-five virtual points have been
30 defined on the plate shape of source 24 in the depicted
example.
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The virtual sound source may be shaped as a set of regular
polygons; as well as shapes that are non-symmetrical,
irregular or organically formed.
Figure 6B illustrates a number of modified audio signal
components that may be used when the virtual sound source has
a two-dimensional or three-dimensional shape. The figure shows
that all modified audio signal components may be time delayed,
and none of the modified audio signal components are inverted
with respect to the input audio signal, in accordance with a
virtual sound source that freely vibrates on all its edges.
Figure /A is a flowchart illustrating an embodiment in
which the generated audio signal y(t) is perceived by an
observer to originate from a sound source that is shaped as a
plate. Again, a plurality of audio signal components y(t) is
determined respectively associated with virtual points that
are defined on the shape. In this embodiment, each
determination of an audio signal component y(t) comprises
modifying the input audio signal using a signal delay
operation introducing a time delay At,1 optionally using a
signal feedback operation 30 in order to obtain a modified
audio signal component. Subsequently, a second modified audio
signal component is generated based on a combination 32 of the
input audio signal and the modified audio signal component.
The second modified audio signal component may be attenuated,
e.g. with approximately -6 dB (see attenuating elements 34).
The second modified audio signal component may be modified
using a signal delay operation At,2 introducing a second time
delay and optionally a signal feedback operation 36 to obtain
a third modified audio signal component. Then, the audio
signal component y(t) may be generated based on a combination
38 of the second and third modified audio signal component.
Optionally, this step of generating the audio signal component
y(t) comprises performing an attenuation operation 40, e.g.
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with -6dB, and/or a high pass filter operation 42 that applies
a cut off frequency of fn, which may be understood to attenuate
frequencies below the lowest fundamental frequency occurring
in the plate.
In this embodiment, determining an audio signal component
comprises determining a first modified audio signal component
and a third modified audio signal component. Determining the
first resp. third modified audio signal component may
comprise using a first resp. second time delay operation and a
signal inverting operation and, optionally, a first resp.
second signal feedback operation.
In this example, two combinations 32 and 38 are performed
per audio signal component, however, for more complex shaped
virtual sound sources, such as three dimensionally shaped
sources, three or even more combination operations are
performed per audio signal component. An example of this is
shown in figure 14.
It should be appreciated that although figure TA shows that
two building blocks 21 are arranged in series for the
generation of each y(t) signal, also more than two, such as
three, four, five, six or even more building blocks 21 can be
arranged in series for the generation of each y(t) signal.
Figure 7B illustrates how for each virtual point on a
virtual sound source 50 that is shaped as a square plate, the
associated time delays and cut-off frequency can be
calculated. As an example, figure 7B illustrates how the time
delays and cut-off frequency is calculated for point n=7 on
the virtual sound source 50 shaped as a plate.
A first step comprises determining, for each virtual point,
three values for the above mentioned multiplication factor x,
viz. xA, x3, xc in accordance with the following formulas:
xA = (1 ' n.A) / 3 ;
R2 I
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n.B
XB =
R2
= (1 /6 for < 0.5 ;
xc = (1¨ rilf) /2 for rnc
U.3 .
Herein R denotes the radius of a circle 52 passing through
the vertices where two or more edges of the virtual sound
source 50 meet. In this example, R is the radius of the
circumscribed circle 52 of the square plate 50.
Further, r,A denotes (see left illustration in figure 7B)
the radius of a circle 56 passing through the vertices of a
square 54, wherein the square 54 is a square having a mid
point that coincides with the mid point of the virtual sound
source 50 and has point n, point 7 in this example, at one of
its sides. The sides of square 54 are parallel to the edges of
the plate 50.
r,B denotes (see middle illustration in figure 7B) the
radius of a circle 60 passing through the vertices of a square
58, wherein the square 58 has a mid point that coincides with
vertex that is nearest to point n and has sides that are
parallel to the edges of the virtual plate sound source 50.
r,c denotes (see right hand side illustration in figure 7B)
the smallest distance between the mid point of the plate 50
and an edge of square 62, wherein square 62 has a mid point
that coincides with the mid point of the virtual sound source
50 and has point n on one of its sides. Further, square 62 has
a side that is perpendicular to at least one diagonal of the
plate A. Since the virtual sound source in this example is
square, square 62 is tilted 45 degrees with respect to the
plate 50.
In a next step, the associated time delays AtA, AtB, Atc are
determined in accordance with At=Ax/v, wherein AtB is only
determined if xB is equal to or smaller than 0.25. Accordingly,
for a square plate having 25 cm long edges and 25 virtual
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points as shown in figures 6A and 7B, and v=500m/s, the values
for xA, Xs, xcandAtA, AtB, Atc are as follows.
n XA XB Xc AtA (5) AtB (5) Atc (5)
1 0 0 0 0 0 0
2 0 0.25 0.125 0 0.003125 0.00156
3 0 1 0.0833 0 0.00104
4 0 0.25 0.125 0 0.003125 0.00156
0 0 0 0 0 0
6 0 0.25 0.125 0 0.003125 0.00156
7 0.25 0.25 0.0833 0.003125 0.003125 0.00104
8 0.25 1 0.125 0.003125 - 0.00156
9 0.25 0.25 0.0833 0.003125 0.003125 0.00104
0 0.25 0.125 0 0.003125 0.00156
11 0 1 0.0833 0 0.00104
12 0.25 1 0.125 0.003125 - 0.00156
13 0.33 1 0.167 0.004167 - 0.00208
14 0.25 1 0.125 0.003125 - 0.00156
0 1 0.0833 0 0.00104
16 0 0.25 0.125 0 0.003125 0.00156
17 0.25 0.25 0.0833 0.003125 0.003125 0.00104
18 0.25 1 0.125 0.003125 - 0.00156
19 0.25 0.25 0.0833 0.003125 0.003125 0.00104
0 0.25 0.125 0 0.003125 0.00156
21 0 0 0 0 0 0
22 0 0.25 0.125 0 0.003125 0.00156
23 0 1 0.0833 0 0.00104
24 0 0.25 0.125 0 0.003125 0.00156
0 0 0 0 0 0
5 As shown, some values of AtA, AtB, Atc are zero, or not
determined because xB >0.25. As a result, for each virtual
point n, one or two different nonzero values are present for
AtA, AtB, Atc. These values are then determined to be Ati and
At2. (See below table).
10 The cut-off frequency for the high pass filter for each
virtual point n may be determined as
V rnA
fc - for - < 0.5 and
A2(1-rnAIR) R
V rnA
f- __________________ for
A2(rnAIR) R
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Thus, for a virtual sound source having a plate shape with
a total surface area A of 625 cm2 which vibrates freely on its
edges and is homogenous in its material structure, the
following values for At and fc may be used.
5
n At1 (s) At2 (s) f. (Hz)
1 0 0 40
2 0.003125 0.00156 53.33
3 0.00104 0 80
4 0.003125 0.00156 53.33
5 0 0 40
6 0.003125 0.00156 53.33
7 0.003125 0.00104 80
8 0.003125 0.00156 53.33
9 0.003125 0.00104 80
10 0.003125 0.00156 53.33
11 0.00104 0 80
12 0.003125 0.00156 53.33
13 0.004167 0.00208 40
14 0.003125 0.00156 53.33
15 0.00104 0 80
16 0.003125 0.00156 53.33
17 0.003125 0.00104 80
18 0.003125 0.00156 53.33
19 0.003125 0.00104 80
20 0.003125 0.00156 53.33
21 0 0 40
22 0.003125 0.00156 53.33
23 0.00104 0 80
24 0.003125 0.00156 53.33
25 0 0 40
Thus, with these values, a user will perceive the generated
audio signal as originating from a plate-shaped sound source
of homogeneous substance and of particular size, whereas the
10 loudspeakers need not be spatially arranged in a particular
manner.
In an embodiment, the method comprises obtaining shape data
representing the virtual positions of the respective virtual
points on the virtual sound source's shape and determining the
15 time delays that are to be introduced by the respective time
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delay operations based on the virtual positions of the
respective virtual points. If the virtual sound source is
shaped as a square plate, then the time delays may be
determined using the formula described above.
Similarly as for 2D shapes, for a 3D shape two or more
modified audio signal components are determined for some or
each of the generated audio signal components y(t) associated
with virtual points that are defined on the shape. The values
for the to be introduced time delays for each virtual point
are in accordance with At=Vx/v, wherein V being the volume of
the shape, wherein x denotes for virtual point n a
multiplication factor according to the radial length rn from
the centre and/or the edges of the shape to point n, and v
relates to the speed of sound through a medium.
For each geometrical shape and/or different materials of
heterogenous substance or material conditions, different
variations of the algorithm may apply in accordance with the
relationship between spatial dimensions of the shape and the
time difference value at each virtual point.
For shapes that are not regular polygons and/or irregularly
shaped, more than two or many modified audio signal components
may be obtained for some or each of the generated audio signal
components yn(t).
Figure 7C illustrates an embodiment that is alternative to
the embodiment of figure 7A. Whereas the embodiment of figure
7A shows two building blocks 21 in series, the embodiment of
figure 7C shows that two building blocks 21 can be arranged in
parallel. The value ax,x in the embodiment of figure 7C is the
same as value ax,x in the embodiment of figure 7A and the value
of bx,x is the same as the value bx,x in the embodiment of figure
7A.
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The embodiment of figure 7C is especially advantageous in
that, for each signal component yi(t), the values of bn.1 and
bn.2 can be controlled independently from each other.
It should be appreciated that although figure 7C shows that
two building blocks 21 are arranged in parallel for the
generation of each y(t) signal, also more than two, such as
three, four, five, six or even more building blocks 21 can be
arranged in parallel for the generation of each y(t) signal.
Figure 7D illustrates an embodiment that is alternative to
the embodiment of figure 7C. Whereas the embodiment of figure
7C shows that two building blocks 21 can be arranged in
parallel, figure 7D shows that, instead of two whole building
blocks, two or more modified audio signals, such as three,
four, five, six or even more, can be generated from the audio
input signal in parallel and then summed, optionally further
modified with an attenuation operation, before being summed
with the audio input signal in order to generate each signal
Yx(t). The value ax,x in the embodiment of figure 7D is the same
as value ax,x in the embodiment of figure TA and figure 7C.
Figure 7D is advantageous in that it enables a more efficient
processing by reducing the amount of signal paths within the
arrangement of the building blocks.
Figure 8 shows (top) the spectrogram of the audio signal
component yi(t) and (second from top) the spectrogram of the
audio signal component y6(t) and (middle) the spectrogram of
the audio signal component y7(t) and (second from bottom) the
spectrogram of the audio signal component yll(t) and (bottom)
the spectrogram of the audio signal component y13(t) indicated
in figure 6A. The values for the time delays and the value of
the frequency cut-off fc may be found in the above table.
Figure RA shows a flow chart according to an embodiment of
the method wherein the generated audio signal will be
perceived by an observer 0 as originating from a sound source
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S that is positioned at a distance, such as a horizontal
distance away from him. The horizontal distance may be
understood as the distance between the perceived virtual sound
source and observer, wherein the virtual sound source is
positioned in front of the observer.
In this embodiment, the input audio signal x(t) is modified
using a time delay operation introducing a time delay and a
signal feedback operation to obtain a first modified audio
signal. Then, a second modified audio signal is generated
based on a combination of the input audio signal x(t) and the
first modified audio signal. The audio signal y(t) is
generated by attenuating the second modified audio signal and
optionally by performing a time delay operation as shown.
Preferably, the time delay that is introduced by the time
delay operation performed for obtaining the first modified
audio signal is as short as possible, e.g. shorter than
0.00007 seconds, preferably shorter than 0.00005 seconds,
more preferably shorter than 0.00002 seconds. Most
preferably, approximately 0.0001 seconds. In case of a digital
sample rate of 96 kHz, the time delay may be 0.00001 seconds.
In dependence of the value of c together with value d, an
observer will perceive different distances between himself and
the virtual sound source. Herein, values in the triangles,
i.e. in the attenuation or amplification operations may be
understood to indicate a constant with which a signal is
multiplied. Thus, if such value is larger than 1, then a
signal amplification is performed. If such value is smaller
than 1, then a signal attenuation is performed. When c=0 and
d=1 no distance will be perceived and when c=1 and d=0 a
maximum distance will be perceived corresponding a relative
distance where the sound source has become imperceptible, and
thus the output of the resulting sum audio signal will be 0 (-
inf db). For performing the signal feedback operation to
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determine the first modified audio signal, the value for d may
relate to the value for c as d=1-cx where the value for x is a
multiplication factor equal to or smaller than 1 applied to
the amount of signal feedback that influences the steepness of
a high-frequency dissipation curve.
In an example, the method comprises obtaining distance data
representing the distance of the virtual sound source. Then,
the input audio signal is attenuated in dependence of the
distance of the virtual sound source in order to obtain the
modified audio signal.
The optional time delay indicated by At2 can create a
Doppler effect associated with movement of the virtual sound
source. At2 may be determined as At2 = L / v, wherein L is a
distance between the sound source S and the observer 0 and v
is the speed of sound through a medium.
Figure 9C, 9D and 9E illustrate alternative embodiments to
the embodiment of figure RA. Herein, the values for c, d and
for the introduced time delay are the same as shown in figure
9B.
Figure 9C differs from the embodiment shown in figure RA in
that the signal delay operation is performed in the signal
feedback operation.
Figure 9D illustrates an embodiment that comprises
modifying the input audio signal to obtain a first modified
audio signal 11 using a signal feedback operation that
recursively adds a modified version 13 of the input audio
signal to itself, wherein the feedback operation comprises a
signal delay operation introducing a time delay. In this
embodiment, the audio signal y(t) is generated based on the
first modified audio signal 11, this step comprising a signal
attenuation 15 and optionally a time delay operation
introducing a second time delay.
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Figure 9E illustrates an embodiment that comprises
generating a second modified audio signal 17 based on a
combination 10 of the first modified audio signal 11 and a
time-delayed version 13 of the first modified audio signal and
5 generating the audio signal y(t) based on the second modified
audio signal thus based on the first modified audio signal.
Fig. 10 (top) shows the spectrogram of sum audio signal
after applying c=0, The input audio signal is white noise.
Here, if c=0 then no modification is visible in the sum audio
10 signal.
Fig. 10 (middle) shows the spectrogram of sum audio signal
after applying c=0.5, The input audio signal is white noise.
The observable result is a decrease of loudness of -12 db and
a gradual damping of higher frequencies, as the perceived
15 distance between the observer and the sound on length L
increases, i.e. the higher frequencies of the sound dissipate
proportionally faster than the lower frequencies. The
curvature of the high-frequency dissipation will increase or
decrease by varying the value x that is smaller than 1 and
20 that multiplies the signal feedback amplitude.
Fig. 10 (bottom) shows the spectrogram of sum audio signal
after applying c=0.99, The input audio signal is white noise.
The overall loudness has decreased -32 db and the steepness of
the high-frequency dissipation curve has increased, rendering
25 the output audio signal close to inaudible, the perceived
effect being as if the sound has dissipated in the distance
almost entirely.
Figure 11A shows a flow chart illustrating an embodiment of
the method when the virtual sound source S is positioned at a
30 virtual height H above an observer 0 (see figure 11B as well).
Herein, the input audio signal x(t) is modified using a signal
inverting operation, a signal attenuation operation and a time
delay operation introducing a time delay in order to obtain a
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third modified audio signal. Then, the audio signal is
generated based on a combination, e.g. summation, of the input
audio signal and the third modified audio signal.
It should be appreciated that the signal delay operation,
the signal inversion operation and the signal attenuation
operation may be performed in any order.
The input audio signal x(t) may be attenuated in dependence
of the height to obtain the third modified audio signal,
preferably such that the higher the virtual sound source is
positioned above the observer, the lower the degree of
attenuation is. This is shown in figure 11 in that the value
for e increases with increasing height of the sound source S.
The introduced time delays as depicted in figure 11A are
preferably as short as possible, e.g. shorter than 0.00007
seconds, preferably shorter than 0.00005 seconds, more
preferably shorter than 0.00002 seconds. Most preferably in
case of a digital sample rate of 96 kHz, the time delay may be
0.00001 seconds
In case the virtual sound source is positioned above a
listener modifying the input audio signal to obtain the third
modified audio signal optionally comprises performing a signal
feedback operation. In a particular example, this step
comprises recursively adding an attenuated version of a
signal, e.g. the signal resulting from the time delay
operation, signal attenuation operation and signal inverting
operation that are performed to eventually obtain the third
modified audio signal, to itself. If the signal feedback
operation is performed, value f may be equal to f=e*x where
the value for x is a multiplication factor smaller than 1
applied to the amount of signal feedback that influences the
steepness of a low-frequency dissipation curve. By varying
value e, preferably between 0-1, a perception of height can be
added to an audio signal, optionally with value f
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simultaneously. Herein, e=0 and f=0 correspond to no perceived
height and e=1 and f<1 to a maximum perceived height, i.e. a
distance above the observer where the sound source has become
close to imperceptible.
Fig. 12A-12C depicts the spectra of audio signals according
to an embodiment of the invention.
Fig. 12A shows the spectrogram of sum audio signal after
applying e=0. The input audio signal is white noise. Here, if
e=0, then no modification is visible in the sum audio signal.
Fig. 12B shows the spectrogram of sum audio signal after
applying e=0.5. The input audio signal is white noise. The
observable result is a gradual damping of lower frequencies,
as the perceived height H of the sound source S above the
observer 0 increases, i.e. the lower frequencies of the sound
dissipate with proportional increase of the value e. The
steepness of the curve of the low-frequency dissipation
increases or decreases by varying the value x that is smaller
than 1 and that multiplies the signal feedback amplitude f.
Fig. 12C shows the spectrogram of sum audio signal after
applying e=0.99, The input audio signal is white noise. The
steepness of the high-frequency dissipation curve has
increased, rendering the output audio signal close to
inaudible for f<12 kHz, the perceived effect being as if the
sound is at a far distance above the head of the perceiver.
Figure 13A shows a flow chart illustrating an embodiment of
the method wherein the virtual sound source S is positioned at
a virtual depth D below an observer 0. (See figure 13B as
well). This embodiment comprises modifying the input audio
signal x(t) using a time delay operation introducing a time
delay, a signal attenuation and a signal feedback operation in
order to obtain a sixth modified audio signal. In the depicted
embodiment, performing the signal feedback operation comprises
recursively adding an attenuated version of a signal, e.g. the
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signal resulting from the time delay operation that is
performed to eventually obtain the sixth modified audio
signal, to itself. For the depicted embodiment this means that
the value for h is nonzero. Preferably, the signal that is
recursively added is attenuated in dependence of the depth
below the observer, e.g. such that the lower the virtual sound
source is positioned below the observer, the lower this
attenuation is (corresponding to higher values for h in figure
13). The attenuation of the input audio signal before the
feedback operation may be performed such that the lower the
virtual sound source is positioned below the observer, the
lower the attenuation (corresponding to higher values for g in
figure 13). Then, the audio signal y(t) is generated based on
a combination of the input audio signal and the sixth modified
audio signal.
The introduced time delay as depicted in figure 13A is
preferably as short as possible, e.g. shorter than 0.00007
seconds, preferably shorter than 0.00005 seconds, more
preferably shorter than 0.00002 seconds. Most preferably in
case of a digital sample rate of 96 kHz, the time delay may be
0.00001 seconds.
When g=0 and h=0 no depth will be perceived and when g=1
and h=1 a maximum depth will be perceived between the sound
source S and the observer 0. For performing the signal
feedback operation to determine the third modified audio
signal, the value for h may relate to the value for g as h=g*x
where the value for x is a multiplication factor equal to or
smaller than 1 applied to the amount of signal feedback, which
influences the steepness of a high-frequency dissipation
curve.
Figures 13C - 13F show alternative embodiments to the
embodiment of figure 13A wherein the virtual sound source is
positioned at a virtual depth below an observer. The values of
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q and the time delay introduced by the signal delay operation
may be the same as in figure 13A.
Figure 13C and 13D are other embodiments that each comprise
modifying the input audio signal x(t) using a time delay
operation 23 introducing a time delay, a first signal
attenuation operation 25 and a signal feedback operation in
order to obtain a modified audio signal and generating the
audio signal based on a combination of the input audio signal
and this modified audio signal. As can be readily seen, the
embodiment of figures 13C and figure 13D differ from the
embodiment of figure 13A in that the signal delay operation
and signal attenuation may or may not be performed in the
signal feedback operation.
Figure 13E shows an embodiment that comprises generating
the audio signal y(t) using a signal feedback operation that
recursively adds a modified version of the input audio signal
to itself, wherein the feedback operation comprises a signal
delay operation 23 introducing a time delay and a first signal
attenuation operation 25.
Figure 13F shows an embodiment wherein a modified audio
signal 11 is determined using a signal feedback operation and
wherein the audio signal y(t) is determined based on a
combination 10 of the modified audio signal and a time
delayed, attenuated version of this modified audio signal.
Fig. 14 depicts a method and system for generating an audio
signal according to an embodiment of the invention. In
particular, Fig. 14 describes a complex flowchart of a spatial
wave transform. Based on input signal x(t) several audio
signal components y(t) are determined, e.g. one for each
virtual point on the virtual sound source's shape. Each audio
signal component y(t) is determined by performing steps that
are indicated in the boxes 70g. Audio signal component yi(t) is
determined by performing the steps as shown in box 701. In each
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box 70n similar steps may be performed, yet while using other
valued parameters.
Figure 14 in particular illustrates an example combination
of several embodiments as described herein. Box 72 comprises
5 the embodiment of figure 7A, however, may also comprise the
embodiments of figure 7C or 7D. Box 74 comprises the
embodiment as illustrated in figure 9A, however it should be
appreciated that any of the embodiments 9C, 9D, 9E may be
implemented in box 74. Box 76 comprises the embodiment as
10 illustrated in figure 11A. Box 78 comprises the embodiment as
illustrated in figure 13A, however any of the embodiments of
respective figures 13C, 13D, 13E and 13F may be implemented in
box 78. Accordingly, the time delays that are introduced by
the time delay operations of box 72 may be determined in
15 accordance with methods described herein with reference to
figures 7A-7D. As described above, the signal inverting
operations in box 72 may only be performed if the virtual
sound source cannot freely vibrate on its edges. In such case,
the high-pass filter 73 is inactive. If the virtual sound
20 source can freely vibrate on its edges, the signal inverting
operations in box 72 are not performed. In such case,
preferably, the high-pass filter is active. The value for the
cut-off frequency may be determined in accordance with methods
described with reference to figures 7A-7D. Further, the
25 parameters c and d and the time delay in box 74 may be valued
and/or varied and/or determined as described with reference to
figures 9A-9E. The parameters e and f may be valued and/or
varied and/or determined as described with reference to
figures 11A and 11B. The parameters g and h may be valued
30 and/or varied and/or determined as described with reference to
figures 13A-13F.
Further, it should be appreciated that building block 21
may be any of the building blocks depicted in figures 1B - 1J.
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In the depicted embodiment, generating an audio signal
component thus comprises adding dimensional information to the
input audio signal, which may be performed by the steps
indicated by box 72, adding distance information, which may be
performed by steps indicated by box 74, and adding height
information, which may be performed by steps indicated by box
76, or depth information, which may be performed by steps
indicated by box 78. Further, a doppler effect may be added to
the input audio signal, for example by adding an additional
time delay as shown in box 80.
Preferably, because a virtual sound source is either
positioned above or below an observer, only one of the modules
76 or 78 is performed. Module 76 can be set as inactive by
setting e=0 and module 78 can be set inactive by setting g=0.
Figure 15 depicts a user interface 90 according to an
embodiment of the invention. An embodiment of the method
comprises generating a user interface 90 as described herein.
This user interface 90 enables a user to input the virtual
sound source's shape,
-respective virtual positions of virtual points on the
virtual sound source's shape,
-the distance between the virtual sound source and the
observer,
-the height at which the virtual sound source is positioned
above the observer,
-the depth at which the virtual sound source is positioned
below the observer.
All functional operations of a spatial wave transform are
translated to front-end user properties, i.e. audible
manipulations of sound in a virtual space. The application of
the invention is in no way limited to the lay-out and of this
particular interface example and can be the subject of
numerous approaches in system design and involve numerous
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levels of control for shaping and positioning sound sources in
a virtual space, nor is it limited to any particular platform,
medium or visual design and layout.
The depicted user interface 90 comprises an input module
that enables a user to control the input audio signal of a
chain using input receives. The input receives may comprise of
multiple audio channels, either receiving from other chains or
external audio sources, together combined as the audio input
signal of a chain. The user interface enables a user to
control the amplification of each input channel, e.g. by using
gain knobs 92.
The user interface 90 may further comprise an output module
that enables a user to route the summed audio output signal of
the chain as an audio input signal to other chains.
The user interface 90 may further comprise a virtual
sound source definition section that enables a user to input
parameters relating to the virtual sound source, such as its
shape, e.g. by means of a drop-down menu 96, and/or whether
the virtual sound source is hollow or solid and/or the scale
of the virtual sound source and/or its dimensions, e.g. its
Cartesian dimensions and/or a rotation and/or a resolution.
The latter indicates how many virtual points are determined
per unit of virtual surface area. This allows a user to
control the amount of required calculations.
The input means for inputting parameters relating to
rotation may be presented as endless rotational knobs for
dimensions x, y and z
The user interface 90 may further comprise a position
sector that enables a user to input parameters relating to the
position of the virtual sound source. the position of the
shape in 3-dimensional space may be expressed in Cartesian
coordinates +/- x, y, z wherein the virtual center of the
space is denoted as 0,0,0; and which may be presented as a
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visual 3-dimensional field that one can place and move a
virtual object within. This 3-dimensional control field may be
scaled in size by adjusting the radius of the field.
The user interface 90 may further comprise an attributes
section 100 that enables a user to control various parameters,
such as the bandwidth and peak level of the resonance,
perceived distance, perceived elevation, doppler effect.
The user interface 90 may further comprise an output
section 102 that enables a user to control the output. For
example, the discrete amplification of each audio signal
component that is distributed to a configured amount of audio
output channels may be controlled. The gain of each
loudspeaker may be automatically controlled by i) the
modelling of the virtual sound source's shape, ii) the
rotation of the shape in 3-dimensional space and iii) the
position of the shape in 3-dimensional space. The method for
distribution of the audio signal components to the audio
output channels may depend on the type of loudspeaker
configuration and may be achieved by any such methods known in
the art.
The output section 102 may comprise a master level fader
104.
The user input that is received through the user interface
may be used to determine appropriate values for the parameters
according to methods described herein.
Fig. 16 depicts a block diagram illustrating a data
processing system according to an embodiment. As shown in Fig.
16, the data processing system 1100 may include at least one
processor 1102 coupled to memory elements 1104 through a
system bus 1106. As such, the data processing system may store
program code within memory elements 1104. Further, the
processor 1102 may execute the program code accessed from the
memory elements 1104 via a system bus 1106. In one aspect, the
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data processing system may be implemented as a computer that
is suitable for storing and/or executing program code. It
should be appreciated, however, that the data processing
system 1100 may be implemented in the form of any system
including a processor and a memory that is capable of
performing the functions described within this specification.
The memory elements 1104 may include one or more physical
memory devices such as, for example, local memory 1108 and one
or more bulk storage devices 1110. The local memory may refer
to random access memory or other non-persistent memory
device(s) generally used during actual execution of the
program code. A bulk storage device may be implemented as a
hard drive or other persistent data storage device. The
processing system 1100 may also include one or more cache
memories (not shown) that provide temporary storage of at
least some program code in order to reduce the number of times
program code must be retrieved from the bulk storage device
1110 during execution.
Input/output (I/O) devices depicted as an input device 1112
and an output device 1114 optionally can be coupled to the
data processing system. Examples of input devices may include,
but are not limited to, a keyboard, a pointing device such as
a mouse, or the like. Examples of output devices may include,
but are not limited to, a monitor or a display, speakers, or
the like. Input and/or output devices may be coupled to the
data processing system either directly or through intervening
I/O controllers.
In an embodiment, the input and the output devices may be
implemented as a combined input/output device (illustrated in
Fig. 16 with a dashed line surrounding the input device 1112
and the output device 1114). An example of such a combined
device is a touch sensitive display, also sometimes referred
to as a "touch screen display" or simply "touch screen". In
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such an embodiment, input to the device may be provided by a
movement of a physical object, such as e.g. a stylus or a
finger of a user, on or near the touch screen display.
A network adapter 1116 may also be coupled to the data
5 processing system to enable it to become coupled to other
systems, computer systems, remote network devices, and/or
remote storage devices through intervening private or public
networks. The network adapter may comprise a data receiver for
receiving data that is transmitted by said systems, devices
10 and/or networks to the data processing system 1100, and a data
transmitter for transmitting data from the data processing
system 1100 to said systems, devices and/or networks. Modems,
cable modems, and Ethernet cards are examples of different
types of network adapter that may be used with the data
15 processing system 1100.
As pictured in Fig. 16, the memory elements 1104 may store
an application 1118. In various embodiments, the application
1118 may be stored in the local memory 1108, the one or more
bulk storage devices 1110, or apart from the local memory and
20 the bulk storage devices. It should be appreciated that the
data processing system 1100 may further execute an operating
system (not shown in Fig. 11) that can facilitate execution of
the application 1118. The application 1118, being implemented
in the form of executable program code, can be executed by the
25 data processing system 1100, e.g., by the processor 1102.
Responsive to executing the application, the data processing
system 1100 may be configured to perform one or more
operations or method steps described herein.
In one aspect of the present invention, the data processing
30 system 1100 may represent an audio signal processing system.
Various embodiments of the invention may be implemented as
a program product for use with a computer system, where the
program(s) of the program product define functions of the
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embodiments (including the methods described herein). In one
embodiment, the program(s) can be contained on a variety of
non-transitory computer-readable storage media, where, as used
herein, the expression "non-transitory computer readable
storage media" comprises all computer-readable media, with the
sole exception being a transitory, propagating signal. In
another embodiment, the program(s) can be contained on a
variety of transitory computer-readable storage media.
Illustrative computer-readable storage media include, but are
not limited to: (i) non-writable storage media (e.g., read-
only memory devices within a computer such as CD-ROM disks
readable by a CD-ROM drive, ROM chips or any type of solid-
state non-volatile semiconductor memory) on which information
is permanently stored; and (ii) writable storage media (e.g.,
flash memory, floppy disks within a diskette drive or hard-
disk drive or any type of solid-state random-access
semiconductor memory) on which alterable information is
stored. The computer program may be run on the processor 1102
described herein.
The terminology used herein is for the purpose of
describing particular embodiments only and is not intended to
be limiting of the invention. As used herein, the singular
forms "a," "an," and the are intended to include the plural
forms as well, unless the context clearly indicates otherwise.
It will be further understood that the terms "comprises"
and/or "comprising," when used in this specification, specify
the presence of stated features, integers, steps, operations,
elements, and/or components, but do not preclude the presence
or addition of one or more other features, integers, steps,
operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and
equivalents of all means or step plus function elements in the
claims below are intended to include any structure, material,
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or act for performing the function in combination with other
claimed elements as specifically claimed. The description of
embodiments of the present invention has been presented for
purposes of illustration, but is not intended to be exhaustive
or limited to the implementations in the form disclosed. Many
modifications and variations will be apparent to those of
ordinary skill in the art without departing from the scope and
spirit of the present invention. The embodiments were chosen
and described in order to best explain the principles and some
practical applications of the present invention, and to enable
others of ordinary skill in the art to understand the present
invention for various embodiments with various modifications
as are suited to the particular use contemplated.
